So was I just wrong about too many litters being bad for them? Theyre cool to breed for an entire year, or when they start having tiny litters?
Yup!
If you feel that a female is struggling to take care of her litters from exhaustion, just give her a break time to time. I'm sure she'll appreciate it.
Other than that, healthy females should be able to breed fine for more than 2 litters.